How do you insulate a livable attic?

A livable attic (heated and occupied) isn't insulated like a standard attic: the insulation goes against the walls and under the roof rather than on the floor, and the method depends on the framing and access. Describe your attic in the quote request to find out what applies to your home.

What's the best way to insulate a house ceiling?

According to Isolation Cornerstone, for a non-livable attic, blowing in fibreglass insulation after sealing air leaks and installing soffit baffles achieves a high insulation level while keeping ventilation functional. This method avoids cold spots and helps reduce heat loss through the top-floor ceiling.

Does vermiculite increase the cost of attic insulation?

Yes, generally, since vermiculite can contain asbestos and must be assessed before any handling. Removing vermiculite before reinsulating the attic is a separate step from blowing in fibreglass, which adds to the project and needs to be priced separately as part of the quote.

How can you benefit from the LogisVert grant for attic insulation?

Hydro-Québec's LogisVert grant has its own eligibility criteria, which include weatherstripping doors and windows in addition to insulation. Isolation Cornerstone can carry out both the weatherstripping and the attic insulation with the same team, but the details and amounts of the financial assistance must be confirmed directly with Hydro-Québec.

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How Much Does It Cost to Insulate an Attic in Montreal

Published November 14, 2026 · 3 min read

Truss attic seen down its length, covered with an even layer of pink blown-in insulation. — Wood trusses lined up one behind the other, and below them a single layer of blown-in insulation, even all the way to the back of the attic.

How much it costs to insulate an attic in Montreal depends on the square footage, the condition of the existing insulation, whether there's vermiculite or mould present, and any air-sealing work needed before blowing in fibreglass insulation. There's no fixed price tag here: a quote made for your attic is the only reliable way to know its actual cost.

What makes the price of attic insulation vary

Before talking numbers, it helps to understand what the job actually involves. In most attics across Greater Montreal, the process goes like this: sealing air leaks, installing a baffle at each soffit to keep ventilation clear, then blowing in fibreglass insulation up to a minimum of R-51. Each of these steps has a cost that varies based on:

the total square footage of the attic to be insulated
how much insulation is already in place and its condition
the number and condition of soffits that need attention
how accessible the attic is (hatch location, height, obstacles)
whether there are multiple air leaks that need to be sealed one by one
whether existing insulation needs to be removed before the new material is blown in

A home with an easy-to-access attic and few leaks will generally cost less to treat than a home with several sections, a complex roof structure, or insulation that needs removing first.

When vermiculite changes the bill

If your attic contains vermiculite, the project doesn't start with blowing in fibreglass. Isolation Cornerstone first assesses this material, since it can contain asbestos, then removes the vermiculite before reinsulating the attic to R-51. This extra step takes time, requires precautions, and involves handling different from standard insulation, all of which directly affects the total project cost.

It's impossible to give a number without having seen the amount of vermiculite present and the area affected.

Mould and ventilation: steps that add to the price

An attic with signs of mould or condensation can't simply get more insulation piled on top. The structure first needs to be decontaminated and treated, then the ventilation and air leaks need to be corrected to prevent the problem from coming back. This combination of work (decontamination, ventilation correction, air sealing) is on top of the insulation itself, and it's one of the reasons two neighbouring homes can receive very different quotes.

If you notice cold rooms upstairs, a rising heating bill, or visible condensation in the attic, these signs should be mentioned right from the quote request to get a price that truly reflects the work required.

The LogisVert grant and weatherstripping

Another factor that affects the project, without necessarily increasing the net cost, is Hydro-Québec's LogisVert grant. The weatherstripping of doors and windows required by this program is done by the same team that handles attic insulation, which simplifies coordinating the eligible work. The exact amounts and conditions of the financial assistance are entirely up to Hydro-Québec: only the program itself can confirm what you're entitled to based on your situation.

Asking for guidance on LogisVert right from the start helps make sure the planned work meets the program's criteria before it even begins.

How to get an accurate price for your attic

Since every attic is different, the only way to get a reliable number is to have the following confirmed in writing (our attic insulation cost page details what drives it):

the exact square footage to be insulated
the target insulation level (minimum R-51)
whether vermiculite, mould, or damage is present
the soffit, baffle, and ventilation work included
whether LogisVert weatherstripping is part of the project

Isolation Cornerstone insulates attics in Laval, in Lanaudière, in the Laurentians, in Montérégie, and in Montreal. You can check our service area to confirm your location is covered, then request a free quote to get a price based on the actual condition of your attic rather than a general estimate.